In vivo limb tissue development in the absence of nerves: A quantitative study

Abstract

The entire presumptive nervous system was excised from early tailbud (Harrison's stage 24) Amblystoma maculatum embryos. For controls, embryos of the same age were operated in an identical manner except that about a 1-mm segment of neural tube dorsal to the presumptive limb buds was left intact. Plastic-embedded, midstylopodium regions of limbs were sampled and the tissues histometrically measured with a TTMC particle counter. The data were statistically analyzed. The results indicated aneurogenic and control limbs to be of equal cross-sectional size at 13 days after the operation. From 21 days to 54 days aneurogenic limbs were from 62 to 75% the size of controls. The development and maintenance of humeri were unaffected by the absence of nerves. Muscle was found to be most sensitive to nerve absence; starting with an equal cross-sectional amount at Day 13 (mostly myoblasts), control muscle increased two- to fivefold, whereas aneurogenic muscle grew feebly from 13 to 21 days and gradually disappeared thereafter. Control muscle was seen with the electron microscope to be normally innervated whereas axons were never found in the aneurogenic animals.